Planar illumination devices generally using discharge tubes, light-emitting diodes (LEDs) and the like as backlight illumination are used for liquid crystal display devices used in display panels and the like. When these planar illumination devices are used in large-size displays and the like, light of high luminance and high chromaticity is required. Thus, in recent years, investigations have been started for constructions using laser light sources.
It is hoped that such display panels are applied to wall-mounted televisions, wherefore there is a strong demand to make display panels larger and thinner and reduce the power consumption thereof.
Since 60% or more of power is consumed for backlight illumination in large-size liquid crystal televisions, it is essential to reduce power consumption of the backlight illumination. In addition to elaboration to improve light utilization efficiency of the backlight illumination, a method for suppressing an emission amount of a light source by finely adjusting the backlight illumination in conformity with a video scene (backlight control) has been proposed and put to practical use as a method for reducing the power consumption. In this backlight control, about 20% of the power consumption of the backlight can be reduced as compared with the case where the backlight is constantly illuminated with a maximum luminance.
As a development of this backlight control, technology for dividing a screen into a plurality of regions and adjusting the luminance of a backlight for each region (local dimming) has also been proposed.
A construction capable of adjusting the luminance of the backlight for each region may be a direct backlight construction in which LED elements are planarly arranged or a construction in which a plurality of edge-light type light guide plates are arranged to permit light to be incident on side surfaces and emitted from principal surfaces, for example, as disclosed in patent literature 1.
Further, a laser projector has been proposed as an image display device for adjusting luminance pixel by pixel (for example, patent literature 2).
However, in the construction in which the LED elements are planarly arranged, it is difficult to make the display panel thinner because a light source and a liquid crystal display panel need to be distant to obtain uniform illumination. If the number of LED elements is increased for thinning, cost becomes a problem.
In the construction disclosed in patent literature 1, if an attempt is made to increase vertical and horizontal partition numbers of the screen to improve the effect of reducing the power consumption, the numbers of fluorescent lamps as light sources and driving circuits also increase, which leads to a considerable cost increase.
The construction disclosed in patent literature 2 is expensive and difficult to make thinner since a considerably large number of optical fibers are required.
In order to modulate luminance pixel by pixel by scanning the screen as disclosed in patent literature 2, the light quantities of light sources need to be modulated at high speed and an external modulator is necessary at least for a green light source. This is because a SHG light source using solid-state laser beam or fiber laser beam as a fundamental wave is generally used for a green laser light source and this type of light source cannot be modulated at high speed. Thus, it is normally necessary to realize the modulation of the green light source by modulating transmittance using an external modulator with the green light source constantly turned on, which does not lead to a reduction of power consumption.
Patent Literature 1:
Japanese Unexamined Patent Publication No. 2007-214142
Patent Literature 2:
Japanese Unexamined Patent Publication No. 2007-140009